What does it mean when it says that the default screensaver module had an unrecoverable error? I've uninstalled and reinstalled Boinc completely and still get the same message.

I've forwarded this to the BOINC developer for the Mac, here's what he answered me:

Charlie Fenton wrote:

Hi Jord,

I cannot reproduce that running BOINC 6.10.58 under OS 10.5.8. And just to make sure that the download has not been corrupted, I downloaded a fresh copy and tested it on both an Intel Mac and a PowerPC Mac.

Does it happen immediately, or after the screensaver has been running a long time? It seems odd that all of a sudden two people are having this problem with a BOINC release that has been around since July.

Note that no one should be running OS 10.5.0, as OS 10.5.8 is a free upgrade which can be downloaded and installed using the Mac's "Software update" command from the Apple Menu.

That error is shown when the screensaver code is not able to start a new thread, which is a very strange error. According to the documentation: "pthread_create() will fail if the system lacked the necessary resources to create another thread, or the system-imposed limit on the total number of threads in a process [PTHREAD_THREADS_MAX] would be exceeded."

The only other thing I can suggest is having them download a fresh copy of the installer from the BOINC web site, or perhaps try BOINC 6.12.9.

Cheers,
--Charlie

So, if you haven't done so yet, first update to OS X 10.5.8, as suggested.
Test to see if that fixes your problems. If it does, great.
If it doesn't, then try with BOINC 6.12.9, which can be downloaded from here. Let us know how you get on, I'll keep the developer in the loop.
____________Jord